Lachie’s faces app has just been blessed with an API:

http://faces.rubyonrails.com.au/users.xml
http://faces.rubyonrails.com.au/users.json
http://faces.rubyonrails.com.au/users/1.xml
http://faces.rubyonrails.com.au/users/1.json
http://faces.rubyonrails.com.au/thankyous.xml
http://faces.rubyonrails.com.au/thankyous.json

and with json callbacky goodness (thanks to drnic):

http://faces.rubyonrails.com.au/users.json?callback=processUsers

Bring on the mashups!